Provided herein are water quality instruments containing multiple sensors for measuring a plurality of water-related parameters. The sensors are uniquely configured to have an extremely high form factor so that they may be contained within a housing that minimizes dead space between sensors and within the housing, with the individual sensor ends forming a single continuous sensing surface. This provides a number of functional benefits in the field of multi-parameter sondes and related sensing methods.
Conventional multi-parameter sondes use a plurality of round or circular sensors that are aligned in a longitudinal direction. With the circular-based geometry, there is substantial dead space or void volume between the sensors, resulting in a number of disadvantages. For example, this dead space must be filled with a fluid in order to ensure appropriate sensor coverage and, therefore, significantly increases the amount of fluid required during sampling. Larger fluid volumes tend to require longer testing times, particularly for low-flow sensing applications, such as sampling from well water. In addition, many sensors require periodic calibration, including prior to data acquisition. This requires a calibration solution and certain calibration solutions are expensive, such as in the $100's/L range.
The large dead space also suffers from the tendency for biological growth to occur in the dead space and on and over the sensors. This is particularly problematic for long deployments, where the large available surface area in long term contact with biologically active water provides a large surface for biological growth, such as from plants, algae and/or animals that anchor to a wetted surface. Multi-parameter sondes with spaced-apart sensors suffer from significant biological growth which must be cleaned to avoid sensor fouling and maintain sensitivity. The open spaces between sensing surfaces makes it difficult to effectively and efficiently automate cleaning, such as with a brush-type wiper.
In view of these limitations, there is a need in the art for fundamentally different sonde configurations and related components that avoid the large open spaces between sensors. Provided herein are sensors with a fundamental change in structure that address the limitations of conventional sonde sensors, and sondes that incorporate the sensors provided herein with additional components that provide fundamental benefits and attendant improved sonde reliability, durability, and sensitivity.